Process for making silicone emulsions

ABSTRACT

In a process for the production of a silicone in water emulsion in which a polysiloxane fluid, at least one surfactant and water are continuously fed to a high shear mixer in such proportions as to form a viscous oil in water emulsion which is continuously withdrawn from the mixer. The polysiloxane fluid may be a non-reactive fluid or may have reactive groups capable of taking part in a chain extension reaction. A desired emulsion particle size can be maintained by monitoring the pressure in the supply line at the inlet to the high shear mixer.

This invention relates to the production of silicone in water emulsionsuseful for example in toiletry and cosmetic products such as shampoosand skin creams, household cleaning products such as liquid detergents,textile process additives such as hydrophilic/hydrophobic modifiers andsofteners, and release agents such as mould release and release coatingsused for example on backings for adhesive products.

Silicone in water emulsions can be produced by emulsion polymerisationor by mechanical emulsification of a silicone polymer with one or moresurfactants and water. Because silicones are highly hydrophobic, stableemulsions are difficult to produce mechanically and it is generallynecessary to mix the silicone with a surfactant and a small amount ofwater under high mechanical shear to form a non-Newtonian “thick phase”,which has a very high viscosity at low shear rates (much more viscous atlow shear rate than the silicone polymer alone) and often exhibits ayield stress (viscoplastic behaviour). The resulting emulsion can bediluted with further water and surfactant. The highly viscous nature ofthis “thick phase” emulsion leads to a risk of uneven mixing orlocalised overheating when the process is carried out batchwise on anindustrial scale.

U.S. Pat. No. 5,504,150 describes preparing emulsions by mixingorganosilicon compounds, with a condensation catalyst and with apressurized gas to cause foaming, feeding the foaming mixture down areactor chamber, forming liquid polymers in the chamber by allowing thecompounds to polymerise in the chamber. After polymerising thecompounds, water and a surfactant are fed to the chamber and mixed withthe foam in the chamber to form a water-in-oil emulsion containing thepolymers. The emulsion is collected at the outlet of the reactor andinverted by shearing to an oil-in-water emulsion.

U.S. Pat. No. 5,806,975 describes a method of continuous emulsificationof high viscosity organopolysiloxane gums in a compounding extruder.JP-A-12-449 describes the continuous production of an organopolysiloxanegrease by feeding an organopolysiloxane with 0.1 to 100% emulsifier and0.5 to 20% water to a rotary disc mixer.

EP-A-874017 describes a method of making a silicone in water emulsioncomprising mixing materials comprising (I) a composition containing atleast one polysiloxane, at least one organosilicon material that reactswith said polysiloxane by a chain extension reaction and a metalcontaining catalyst for said chain extension reaction, (II) at least onesurfactant and (III) water to form a mixture; and emulsifying themixture.

EP-A-915122 describes a process for preparing a silicone latex. Theprocess comprises forming a premix of polydiorganosiloxane andcrosslinker and then forming silicone latex by mixing surfactant andwater with the premix. A process for the continuous preparation of thesilicone latex using in-line dynamic mixers is also described.

In a process according to a first aspect of the present invention forthe production of a silicone in water emulsion, in which a polysiloxanefluid, at least one surfactant and water are continuously fed to a highshear mixer in such proportions as to form a viscous oil in wateremulsion which is continuously withdrawn from the mixer, thepolysiloxane, the surfactant and the water are fed into the high shearmixer through a single supply line and the pressure in the supply lineat the inlet to the high shear mixer is monitored to be within 20% of atarget pressure predetermined to give a desired emulsion particle size.

We believe that in the high shear mixer a crude water in oil premix isinitially formed which is continuously transformed into the “thickphase” oil in water emulsion by the high shear conditions applied in themixer.

We have found that in such a continuous process, the pressure at theinlet to the mixer correlates to the particle size of the emulsioneventually formed. The target pressure corresponding to a desiredemulsion particle size is specific to each process/apparatus andcomposition, but can readily be determined by experiment. When theprocess is running continuously and the polysiloxane fluid, surfactantand water are being fed at a constant rate, the inlet pressure is ameasure of the resistance to flow in the mixer. We have found that avariation of this inlet pressure by over 20% (in many cases a variationof over 10%) corresponds to a variation in the particle size of theemulsion product which is generally much greater than 20% and could evenindicate that transformation into an oil in water emulsion is not takingplace. The pressure in the supply line is preferably monitoredcontinuously. If such a variation, particularly a drop in pressure, isobserved or recorded, the process can be adjusted to restore thepressure level, for example by a slight increase in the proportion ofsurfactant fed to the mixer or by diverting the mixer outlet to scrapand stopping the continuous process. Automatic controls can be arrangedto take such a step when a significant pressure variation occurs or aprocess operator can act when the pressure variation is noted.

The polysiloxane fluid can for example have a viscosity of at least0.001, preferably at least 0.02 Pa.s up to 1000 Pa.s (1 or 20 up to1000000 cps) or even up to 20000 Pa.s. The process of the invention isparticularly suitable for continuous emulsification of substantiallylinear polydiorganosiloxanes such as polydimethylsiloxane althoughbranched and/or cyclic polysiloxanes can also be emulsified. Thepolysiloxane fluid may be a non-reactive fluid, for example a linearpolysiloxane tipped with trimethylsiloxy units, or may be a reactivefluid having reactive groups such as hydroxyl (either Si—OH or alcoholgroups), amino, vinyl or Si—H groups. A reactive fluid may be reactedduring or after the emulsification process as described in more detailbelow.

The surfactant can in general be any surfactant known for emulsificationof silicones and can be a cationic, anionic, nonionic and/or amphotericsurfactant. Mixtures of surfactants of different types and/or differentsurfactants of the same type can be used. Combinations of ionicsurfactants and nonionic surfactants may be particularly preferred. Formany uses the surfactant needs to be chosen to give optimumcompatibility with the product into which the silicone emulsion is to beincorporated.

Examples of non-ionic surfactants include polyoxyalkylene alkyl etherssuch as polyethylene glycol long chain (9-22C, especially 12-14C) alkylether, polyoxyalkylene sorbitan ethers, polyoxyalkylene alkoxylateesters, polyoxyalkylene alkylphenol ethers, ethylene oxide propyleneoxide copolymers, polyvinyl alcohol, glyceride esters andalkylpolysaccharides.

Examples of cationic surfactants include quaternary ammonium salts suchas 8-22C alkyl trimethyl ammonium halides, particularly chlorides, 8-22Calkyl dimethyl benzyl ammonium halides or di(8-22C alkyl) dimethylammonium halides where the 8-22C alkyl group is for example octyl,decyl, dodecyl, hexadecyl, oleyl or octadecyl or tallow or coco alkylgroups, as well as corresponding salts of these materials, fatty aminesand fatty acid amides and their derivatives, basic pyridinium compounds,quaternary ammonium bases of benzimidazolines andpoly(ethoxylated/propoxylated) amines. Methosulphates, phosphates oracetates can be used as an alternative to halides.

Examples of suitable anionic surfactants include alkyl sulfates such aslauryl sulfate, polymers such as acrylates/C₁₀₋₃₀ alkyl acrylatecrosspolymer, (6-20C alkyl) benzenesulfonic acids and salts, the sulfateesters of monoalkyl polyoxyethylene ethers, sulphonated glyceryl estersof fatty acids, salts of sulphonated monovalent alcohol esters, amidesof amino sulphonic acids, sulphonated products of fatty acid nitriles,condensation products of naphthalene sulphonic acids with formaldehyde,alkali metal alkyl sulphates and ester sulphates, alkyl phosphates,sarcosinates and sulphonated olefins.

Examples of suitable amphoteric surfactants include cocamidopropylbetaine, cocamidopropyl hydroxysulphate, cocobetaine, sodiumcocoamidoacetate, cocodimethyl betaine, N-coco-3-aminobutyric acid andimidazolinium carboxyl compounds.

Some anionic surfactants such as sulphonates and sulphates, for examplealkyl benzene sulphonic acids, have some catalytic activity forcondensation polymerisation of polysiloxanes, particularlysilanol-functional polydiorganosiloxanes such as hydroxyl-terminatedpolydimethylsiloxanes, with themselves or in copolymerisation withorganic or silane monomers and/or polymers having condensablefunctionality such as hydroxyl groups. The catalytic activity can besuppressed by a neutralising agent such as an organic amine, for exampletriethanolamine, or an inorganic base such as sodium hydroxide. It isusually preferred to avoid polymerisation before formation of theemulsion in the high shear mixer, because uncontrolled polymerisationmay increase the viscosity of the polysiloxane so that it becomes toohigh to be properly emulsified when passing through the mixer. Inaddition, neutralization avoids corrosion and/or minimizes the need forspecial acid-resistant materials of construction for processingequipment. Subsequent acidification by addition of an acid or ionexchange, for example, treatment with an acidic ion exchange resin, willreactivate the catalytic properties of the sulphonate or sulphatesurfactant if required.

Some cationic surfactants such as quaternary ammonium salts may alsohave catalytic activity for condensation polymerisation ofpolysiloxanes, particularly silanol-functional polydiorganosiloxanessuch as hydroxyl-terminated polydimethylsiloxanes, with themselves or incopolymerisation with organic or silane monomers and/or polymers havingcondensable functionality such as hydroxyl groups. The catalyticactivity may be activated by addition of an acid or base.

The surfactant can be added undiluted to the polysiloxane fluid or oneor more surfactant can be premixed with water. Some surfactants are soldin aqueous form. The amount of surfactant added in the supply line tothe high shear mixer is generally at least 0.2% by weight based on thepolysiloxane fluid, preferably at least 0.5%, for example from 2% up to10 or 20%. The amount of water present, including any water present inthe surfactant composition, is generally at least 0.5% based on thepolysiloxane fluid, preferably at least 1% up to 10 or 20% or even 30%.The polysiloxane content of the mixture fed into the high shear mixer ispreferably from 70 to 99% by weight, most preferably 80 to 98%.

Where more than one surfactant is used, the surfactants can in generalbe premixed or can be added successively to the polysiloxane fluid. Wehave found that when an ionic (anionic or cationic) and a nonionicsurfactant are used, an emulsion of lower and less variable particlesize can be produced if the ionic surfactant is contacted with thepolysiloxane fluid before it contacts the nonionic surfactant.

Thus according to another aspect of the invention a process for theproduction of a silicone in water emulsion, in which a polysiloxanefluid, at least one surfactant and water are continuously fed to a highshear mixer in such proportions as to form a viscous oil in wateremulsion which is continuously withdrawn from the mixer, ischaracterised in that the polysiloxane fluid is contacted successivelywith an ionic surfactant and then with a non-ionic surfactant beforebeing fed to the high shear mixer.

The polysiloxane fluid and the ionic surfactant are preferably mixedbefore contacting the non-ionic surfactant, for example they can bepassed through a static mixer to achieve dispersion of the ionicsurfactant throughout the polysiloxane before the non-ionic surfactantis added.

The “thick phase” oil in water emulsion which is continuously withdrawnfrom the high shear mixer usually needs to be diluted to reduce itsviscosity before use. The “thick phase” can be diluted eithercontinuously or batchwise. The amount of water added at this stage isgenerally at least 10% and preferably at least 20% based on thepolysiloxane fluid, for example 30 to 150%. Further surfactant can beadded at the dilution stage if desired, for example up to 10% by weightsurfactant based on the polysiloxane fluid. The surfactant can bepremixed with the water used for dilution or can be added separately.After addition of the water and optionally surfactant, the emulsion isthoroughly mixed, preferably in a high shear mixer, to ensure that ithas been fully homogenised. If a more dilute emulsion than about 40%silicone is required, further water is preferably added in a subsequentdilution step which requires less vigorous mixing conditions.

The invention will now be described with reference to the single Figureof the accompanying drawings, which is a diagrammatic flow chart of theprocess of the invention.

Polysiloxane fluid is fed through main feeding line (1). A secondaryfeeding line (2) can be used for feeding a second polysiloxane, forexample a polysiloxane which is reactive with the main polysiloxanefluid or forms a blend with it. A third feeding line (3) can be used forany other material to be blended with the polysiloxane, for example acatalyst for a reactive system. The polysiloxane and any materials fedthrough lines (2) and (3) are mixed in premixer (4), which is preferablya dynamic mixer but is for mixing purpose and has no special shearrequirement. The secondary feed lines (2, 3) and mixer (4) can beomitted when producing emulsions from a single polysiloxane fluid.

The conduit (5) for polysiloxane fluid leaving mixer (4) forms a supplyline leading towards high shear dynamic mixer (9). The supply line (5)is fed by first surfactant feeding line (6), second surfactant feedingline (7) and water feeding line (8). The order of injection ofsurfactants and water between lines (6, 7 and 8) can be changeddepending on the formulation. Only one surfactant may be used, in whichcase one feed line (7) is not required. One of the surfactants may alsoalready be diluted in water in which case it is possible that line (8)is not used. Main supply line (5) and those feed lines (6, 7 and/or 8)which are in use are all arranged to give continuous stable dosing ofthe material being fed, for example they preferably incorporate constantdelivery pumps and may have back pressure valves between each pump andthe main feed line (5). A mixer, for example a static mixer, may beincluded in supply line (5) between feeds (6 and 7) and/or between feeds(7 and 8). If a neutralising agent such as an amine is added to suppressthe catalytic activity of an anionic surfactant, it can for example beadded with that surfactant or added to the polysiloxane fluid, forexample in feed line (2 or 3) before it contacts the surfactant.

The high shear dynamic mixer (9) used to emulsify the polysiloxanefluid, surfactant and water to a viscous oil in water emulsion can forexample be an in-line, dynamic rotor/stator device such as those soldunder the Trade Marks “TK Products Homomic Line Mill” or “Bematek” or“Greerco” or “Ross”, often referred to as a colloid mill, or a rotarydisc mixer of the type described in JP-A-2000-449, or a twin screwcompounder of the type used for plastics extrusion. The mean residencetime of the polysiloxane fluid mixture in the mixer (9), based on thetotal free volume in the body of the mixing device, is preferablybetween 0.1 and 600 seconds, particularly 1 to 60 seconds, and thedegree of shear exerted by mixer (9) should be sufficient to emulsifythe polysiloxane within this time. The residence time in the shear gapof an in-line rotor/stator mixer is preferably between 0.001 and 1seconds, particularly 0.005-0.05 seconds. The circumferential speed ofthe mixer is preferably between 0.6 and 60 m/s, particularly 2-20 m/s.The emulsion produced in mixer (9) generally exhibits non-Newtonianfluid behaviour and has a substantially higher low shear viscosity thanthe polysiloxane fluid that it contains. The viscous emulsion isdischarged from mixer (9) through thick phase transfer line (10).

A pressure sensor (P) is located in the supply line (5) at the inlet tomixer (9). The sensor (P) can be a pressure gauge of any type known inthe chemicals industry for measuring pressure in continuously flowingliquids. For a given process system, emulsion composition, and totalprocess flow rate, the pressure measured by (P) can be correlated withparticle size of the emulsion produced and a target pressure determined.The pressure at (P) is preferably monitored continuously to check thatit is within 20%, preferably within 10%, of the target pressure. We havefound that maintaining the back pressure (P) within these limits isindicative of an emulsion of relatively uniform particle size so that90% of the particles in the emulsion product have a size below 3M,usually below 2M, where M is the volume-based median size of theparticles in the emulsion. The variation in particle size is much lessthan the variation found when using direct batch emulsification, forexample by high pressure homogeniser. Routine testing of emulsionparticle size can be reduced; in general, testing is only necessary ifthere has been a significant drop in back pressure (P).

The target pressure can be any pressure from 0.05 up to 20 or 40 bar oreven higher, if the mechanical pressure constraints of the processallow. For forming an emulsion of particle size in the range 0.03 or 0.1or 0.15 microns up to 20 microns, particularly a submicron particle sizeemulsion, from a nonreactive linear polysiloxane fluid, using apparatussuch as that described in FIG. 1 and the conditions of Example 1, thetarget pressure is preferably in the range 2 to 20 bar, most preferably4 to 6 bar.

A modular valve (11) is positioned in the thick phase transfer line(10). This valve (11) can be used to increase the pressure in line (10)and through mixer (9). It is not generally needed and is usually openwhen the process is running continuously in a steady state, but valve(11) is partially closed to increase pressure in line (10) and hence tocontrol the back pressure (P) during start up when producing emulsionsfrom a low viscosity polysiloxane, for example a fluid having aviscosity below 2 Pa.s.

A dilution water feeding line (12), an optional surfactant post-additionfeed line (13) and an optional powder additive dosing line (14) all feedinto the thick phase transfer line (10). In many cases the viscous oilin water emulsion is diluted with water alone, or the surfactant isincorporated in the water feed line (12), so that feed lines (13) and(14) may not be used. Surfactant used in dilution can be of any of thetypes described above. The thick phase, water and optional additivespass to a high shear dynamic mixer (15) in which the emulsion isdiluted, for example to a silicone content of 60% by weight, andinverted to an oil in water emulsion. The mixer (15) can be of any ofthe types described above as suitable for mixer (9).

If an amine has been added before emulsification to suppress thecatalytic activity of a sulphonate or sulphate surfactant, an acid canbe added to the dilution water in feeding line (12) if it is desired toreactivate the catalytic properties of the sulphonate or sulphatesurfactant. Alternatively an acid can be added, or the emulsion can betreated with an acidic ion exchange material, after dilution in themixer (15).

The resulting oil in water emulsion is withdrawn from mixer (15) throughtransfer line (16). If a high silicone content emulsion, for example anemulsion of silicone content at least 40 or 50% by weight, is required,the line (16) can fed directly to the container in which the emulsion isto be sold or transported. If a more dilute emulsion is required, watercan be added through final water addition line (17). Further feed lines(such as 18, 19, 20) for additives such as thickener, preservativesand/or antifoam can be used. Alternatively, further feed lines could beconnected into transfer line (10) before the first dilution mixer (15)if the required formulation is of high silicone content. If water oradditives have been added from any of feed lines (17 to 20) the emulsionpasses through a dynamic mixer (21) used to ensure even dilution. Themixer (21) can be of a type as described above or may be of a moresimple type, since mixing is its only purpose and high shear is notrequired. The emulsion issuing from mixer (21) through line (22), whichhas the silicone level required by a customer, passes to a containersuch as a drum, tote or road tanker.

In an alternative embodiment of the invention, the process can be workedin semi-continuous mode. In this embodiment, the feed lines (12 to 14and 17 to 20) and mixers (15, 21) can be omitted and the viscous oil inwater emulsion in thick phase transfer line (10) downstream of valve(11) can be charged to an agitated dilution tank containing dilutionwater and any required additives. It may be possible for someformulations to feed the viscous emulsion produced in mixer (9) directto containers in which it is shipped for dilution, for example by acustomer whose products are in aqueous emulsion form.

In another alternative embodiment, the mixers (9 and 15) can be combinedin a single apparatus such as a double disc refiner allowing injectionof water between two mixing chambers. Alternatively the mixers (9, 15and optionally 21) can be different barrels of a twin screw compounderallowing addition of water and other materials between barrels. A twinscrew compounder may be the preferred mixer when handling polysiloxanefluids of very high viscosity, for example at least 1000 Pa.s., and isalso suitable for emulsifying low viscosity fluids.

If the polysiloxane fluid contains reactive groups, it may undergo achain extension reaction during the emulsification and dilution process.The materials to be emulsified can also comprise an organosiloxanematerial that reacts with the polysiloxane, preferably by a chainextension reaction. Such an organosiloxane material can for example befed through line (2).

The invention thus includes a process for making a silicone in wateremulsion comprising mixing a polysiloxane fluid having reactive groupscapable of taking part in a chain extension reaction, a catalyst forsaid chain extension reaction, at least one surfactant and water andoptionally an organosiloxane material that reacts with said polysiloxaneby a chain extension reaction to form a mixture and emulsifying themixture, characterized in that the polysiloxane fluid, at least onesurfactant and water are continuously fed to a high shear mixer in suchproportions as to form a viscous oil in water emulsion which iscontinuously withdrawn from the mixer, the catalyst and theorganosiloxane material (if used) each being added either before orafter the mixture is fed to the high shear mixer.

Examples of chain extension reactions are the hydrosilylation reactionin which a Si—H group reacts with an aliphatically unsaturated group inthe presence of a platinum or rhodium containing catalyst, or thereaction of an Si—OH group with an alkoxy group present in analkoxysilane, silicate or alkoxysiloxane, or a CH₃COOSi—, R₂C═NOSi orSiH group in the presence of a metal containing catalyst, or thereaction of a Si—OH group with another Si—OH group in the presence of anacid catalyst, which can be an anionic surfactant as described above.The polysiloxane used in such reactions preferably comprises asubstantially linear polymer, for example a polydiorganosiloxane, inwhich on average there is between one and two reactive groups perpolymer and a majority, more preferably over 90%, and most preferablyover 98% of the reactive groups are end-groups. The organosiloxanematerial that reacts with the polysiloxane by a chain extension reactioncan be either a second polysiloxane or a material that acts as a chainextension agent. Preferably it is a linear polydiorganosiloxane in whichat least a majority of its reactives are end-groups.

The catalyst in such a process can be added through line (3) andpremixed with the polysiloxane in mixer (4), in which case a chainextension reaction may start in feed line (5) and mixer (9). The feedline (5) can be cooled, for example to about 0° C., to minimise suchreaction. It may be preferred to add the catalyst to the emulsion afterthe emulsion has been formed in the high shear mixer (9). The catalystcan for example be incorporated in the water or aqueous surfactant addedthrough line (12), which dilutes and inverts the emulsion, or withsurfactant added through line (13), or can be added separately to thethick phase (10) through a feed such as (14). Addition through line (13)as a mixture with non-ionic surfactant has been found to be aparticularly effective way of incorporating catalyst. Alternatively thecatalyst can be incorporated in the surfactant feed (6 or 7) and/or thewater feed (8) which contacts the organopolysiloxane feed (5) before thehigh shear mixer (9).

In a further alternative which is possible if the catalyst does notcatalyse self-polymerisation of the polysiloxane, the catalyst can beadded to the polysiloxane fluid through feed (3) or incorporated in feed(6, 7 or 8), with the organosiloxane material (chain extender) beingadded after the mixer (9). An example of such a catalyst is ametal-containing catalyst, particularly a platinum or rhodium containingcatalyst, used with a vinyl terminated polydiorganosiloxane fluid and aSi—H terminated polydiorganosiloxane as the organosiloxane materialco-reactant.

The invention is illustrated by the following Examples, in which partsand percentages are by weight.

EXAMPLES 1 and 2

These Examples describe the preparation of an emulsion from ahydroxy-terminated polydimethylsiloxane fluid of viscosity 60 Pa.s. BothExamples prepared a thick oil in water emulsion continuously in a highshear dynamic mixer (9). In Example 1 the thick phase was dilutedbatchwise in a dilution tank. In Example 2 the thick phase was dilutedcontinuously. The amounts of materials added through different lines areshown in Table 1 below. TABLE 1 Example 1 Example 2 Reference ReferenceMaterial Weight % in FIG. Weight % in FIG. Polysiloxane fluid 60 1 = 560 1 = 5 Cocoalkyl 1.9 6 1.9 6 pentaethoxy methyl ammonium methosulphate(pure cationic surfactant) Coco trimethyl 1.93 7 1.93 7 ammoniummethosulfate (30% active aqueous cationic surfactant) Coco trimethyl5.87 Dilution 5.87 13 ammonium tank methosulfate (30% active)Demineralised 29.2 dil tank 21.6 12 water Demineralised 7.6 17 waterSilicone antifoam 0.1 dil tank 0.1 18 Glycacil L 0.1 dil tank 0.1 19(preservative) Phenoxyethanol 0.9 dil tank 0.9 20 (preservative)

The premix mixer (4) was not used. The high shear dynamic mixer (9) wasa Homomic Line Mill running at 3800 rpm and a circumferential speed of20 m/s with a rotor/stator with a gap of 0.5 mm. The pressure (P) at thehigh shear dynamic mixer inlet was maintained at about (within 10% of) 5bars. During start-up an excess of the diluted surfactant feed (7) wasused and the back pressure was increased as necessary by modular valve(11). When the feed rates were at the rates shown above the requiredpressure could be maintained with valve (11) open. The residence time ofthe polysiloxane in mixer (9), based on the total volume of the mixerbody, was about 8 seconds.

In Example 1, the process was operated continuously for long enough toproduce sufficient thick oil in water oil emulsion for one batch, thenthe continuous part of the process was stopped. The dilution tank wasagitated at 50 rpm and dilution was continued for 3 hours.

In Example 2, the high shear dilution mixer (15) was a Homomic Line Millrunning at about 3500 rpm and a circumferential speed of 18 m/s with agap of 0.5 mm. The second dilution mixer (21) was a Delmotte (TradeMark) standard in-line dynamic mixer running at about 1500 rpm.

The non-volatile content of the emulsion produced was 65%. Thevolume-based median particle size D(v,0.5) was 0.38 microns in bothExamples as measured by laser diffraction. The particle size of theemulsion produced in Example 1 was analysed and D(v,0.9) was 0.85microns, i.e. 90% of the particles have particle size below 0.85microns.

EXAMPLES 3 and 4

Emulsions were produced by the process of EP874017 in which a chainextension reaction is carried out during emulsification. In bothExamples the polysiloxane fluid comprised a vinyl-terminated linearpolysiloxane of viscosity 10 Pa.s and a SiH-terminated short chainlinear polysiloxane of viscosity 10 mpa.s. Both Examples prepared athick oil in water emulsion continuously in a high shear dynamic mixer(9), although this emulsion was less viscous than the thick phase ofExample 1. In Example 3 the thick phase was diluted batchwise. InExample 4 the thick phase was diluted continuously. The amounts ofmaterials added through different lines are shown in Table 2 below.TABLE 2 Example 3 Example 4 Reference Reference Material Weight % inFIG. Weight % in FIG. Vinyl polysiloxane 65 1 65 1 SiH polysiloxane 2.042 2.04 2 Hexadecyl 7.8 6 7.8 6 trimethyl ammonium chloride (29% activeaqueous cationic surfactant) Demineralised 10 8 10 8 water Demineralised14 dilution 14 12 water tank Platinum complex 0.031 dil tank 0.031 13catalyst dispersed of of in non-ionic active active surfactant/waterPlatinum platinum mixture Cellulosize 1 dil tank 1 14

The premix mixer (4) was a Delmotte mixer running at 1500 rpm. The highshear dynamic mixer 9 was a Homomic Line Mill running at 3000 rpm and acircumferential speed of 16 m/s with a rotor/stator gap of 0.5 mm. Thepressure (P) at the high shear dynamic mixer inlet was 0.2 bars.

In Example 3, the continuous process was operated for a time to producesufficient thick phase for one batch, then the continuous part of theprocess was stopped. The dilution tank was agitated at 50 rpm anddilution was continued for 1 hours. The median particle size of the oilin water emulsion produced was 10 microns and D(v,0.9) was measured as20 microns.

In Example 4, the first high shear dilution mixer (15) was a HomomicLine Mill running at about 2000 rpm and a circumferential speed of 11m/s with a rotor/stator gap of 0.5 mm. The second dilution mixer 21 wasnot used.

EXAMPLES 5 and 6

Following the general procedure of Example 1, a thick phase silicone oilin water emulsion was produced from a trimethylsilyl-terminatedpolydimethylsiloxane fluid of viscosity 1 Pa.s by feeding theingredients shown in Table 3 below. A static mixer was inserted in line(5) after surfactant feed (6) and before surfactant feed (7) so that thesurfactant added at (6) was pre-dispersed in the polysiloxane fluid.TABLE 3 Example 5 Example 6 % by Reference % by Reference weight in FIG.weight in FIG. Polysiloxane 86.0 1 86.0 1 fluid Sodium N- 6.5 6 6.5 7lauroyl sarcosinate 35% aqueous anionic surfactant Tridecanol 7.5 7 7.56 ethoxylate(7) 85% aqueous nonionic surfactant

The thick phase was diluted in a dilution tank as described inExample 1. Particle size analysis of the emulsions produced gave thefollowing results:

-   -   Example 5—Median Particle Size 212 nm, D(v0.9) 275 nm    -   Example 6—Median Particle Size 247 nm, D(v0.9) 400 nm

As can be seen from the above results, stable emulsions were produced inboth Examples 5 and 6, but a lower and more uniform particle size wasproduced in Example 5 where the polysiloxane was premixed with theanionic surfactant before addition of the nonionic surfactant.

EXAMPLES 7 to 9

Silicone emulsions were produced using the general procedure andingredients of Example 5, but in the relative proportions 87.7%polysiloxane fluid, 4.9% anionic surfactant and 7.4% aqueous nonionicsurfactant. In Example 7 no mixer was used between surfactant feeds (6)and (7). In Example 8 there was medium mixing of the anionic surfactantand polysiloxane fluid (simple static mixer between feeds (6) and (7)).In Example 9 there was thorough mixing of the anionic surfactant and thepolysiloxane fluid (dynamic mixer between feeds (6) and (7)). Stableemulsions were produced in all Examples. The mean particle sizes of theemulsions were:

-   -   Example 7—254 nm    -   Example 8—197 nm    -   Example 9—188 nm

EXAMPLE 10

A silicone emulsion was produced by a semi-continuous process of thetype described in Example 1 from the materials listed in Table 4 belowadded at the points shown. TABLE 4 % by weight Reference in FIG.Polysiloxane OH- 91.7 1 terminated fluid Triethanolamine 4.6 3 Sodiumdodecyl 3.7 6 benzene sulphonate anionic surfactant Water 8 8

Particle size analysis of the emulsion produced showed median particlesize 173 nm and D(v0.9) 259 nm.

EXAMPLE 11

Following the process of Example 10, a silicone emulsion was produced bya semi-continuous process from the materials listed in Table 5 belowadded at the points shown TABLE 5 % by weight Reference in FIG.Polysiloxane OH- 89.4 1 terminated fluid of viscosity 0.065 Pa · sTriethanolamine 3.39 3 Dodecylbenzene 4.74 6 sulphonic acid anionicsurfactant Water 2.47 8

Particle size analysis of the emulsion produced showed:

-   -   Example 10—D(v,0.5) 173 nm and D(v,0.9) 259 nm.    -   Example 11—D(v,0.5) 196 nm and D(v,0.9) 272 nm.

EXAMPLES 12 and 13

A silicone emulsion was produced by a semi-continuous process of thetype described in Example 1 from the materials listed in Table 5 belowadded at the points shown. The Homomic Line Mill was operated at arotor/stator gap of 0.35 mm, at a circumferential speed of 16 m/s. TABLE6 % by weight (Ex. 12/Ex. 13) Reference in FIG. Polysiloxane OH-85.6/89.4 1 terminated fluid of viscosity 0.065 Pa · s Triethanolamine5.35/4.60 3 Dodecylbenzene 7.47/4.70 6 sulphonic acid surfactant Water1.58/1.30 8

Particle size analysis of the resulting emulsions by dynamic lightscattering showed particle size:

-   -   Example 12: D(v,0.5) 120 nm and D(v,0.9) 185 nm.    -   Example 13: D(v,0.5) 144 nm and D(v,0.9) 270 nm.

1. A process for the production of a silicone in water emulsion in whicha polysiloxatle fluid, at least one surfectant and water arecontinuously fed to a high shear mixer in such proportions as to form aviscous oil in water emulsion which is continuously withdrawn from themixer, characterised in that the polysiloxane, the surfactant and thewater are fed into the high shear mixer through a single supply line andthe pressure in the supply line at the inlet to the high shear mixer ismonitored continuously, and adjusted if required, to be within 20% of atarget pressure predetermined to give a desired emulsion particle size.2. A process according to claim 1 characterised in that the targetpressure is in the range 2 to 20 bar and the volume-based medianparticle size of the oil in water emulsion product is in the range 0.03to 20 micrometres.
 3. A process according to claim 2, chamacterised inthat the target pressure is in the range 4 to 6 bar and the medianparticle size of the product is in the range 0.1 to 1.0 micrometres. 4.A process for the production of a silicone in water emulsion in which apolysiloxane fluid, at least one surfactant and water are continuouslyfed to a high shear mixer in such proportions as to form a viscous oilin water emulsion which is continuously withdrawn from the mixer,characterised in that the polysiloxane fluid is contacted successivelywith an ionic surfactant and then with a non-ionic surfactant beforebeing fed to the high shear mixer.
 5. A process according to claim 4,characterised in that the polysiloxane fluid and ionic surfactant aremixed before being contacted with the non-ionic surfactant.
 6. A processaccording to any of claims 1 to 5, characterised in that thepolysiloxane content of the mixture fed into the high shear mixer isfrom 70 to 99% by weight.
 7. A process according to any of claims 1 to6, characterised in that the surfactant and water are fed separately tothe silicone in the supply line.
 8. A process according to any of claims1 to 6 characterised in that at least part of the water is added in theform of an aqueous surfactant solution to the silicone in the supplyline.
 9. A process according to any of claims 1 to 8, characterised inthat the viscosity of the polsiloxane fluid is in the range 0.001 to1000 Pa.s.
 10. A process according to claim 9, characterised in that theviscosity of the polysiloxane fluid is less than 2 Pa.s and in that thepressure in the supply line is increased by a modular valve positioneddownstream of the high shear mixer.
 11. A process according to any ofclaims 1 to 10, characterised in that 90% of the particles in theemulsion product have a size below 3M, where M is the median size of theparticles in the emulsion.
 12. A process according to any of claims 1 to11, characterised in that the polysiloxane fluid contains reactivegroups.
 13. A process according to claim 12, characterised in that thepolysiloxane fluid is a silanol-functional polydiorganosiloxane and thesurfactant is an anionic surfactant having catalytic activity forpolymerisation of the silanol-functional polydiorgnosiloxane.
 14. Aprocess according to claim 13, characterised in that an amineneutralising agent is contacted with the polysiloxane fluid and anionicsurfactant to avoid polymerisaion before formation of the emulsion inthe high shear mixer.
 15. A process for the production of a silicone inwater emulsion in which a polysiloxane fluid, at least one surfactantand water are continuously fed to a high shear mixer in such proportionsas to form a viscous oil in water emulsion which is continuouslywithdrawn from the mixer, characterised in that the polysiloxane fluidis a silanol-functional polydiorganosiloxane and the surfactant is ananionic surfactant having catalytic activity for polymerisation of thesilanol-functional polydiorganosiloxane and in that a neutralising agentis contacted with the polysiloxane fluid and anionic surfactant to avoidpolymerisation before formation of the emulsion in the high shear mixer.16. A process according to claim 14 or claim 15, characterised in thatthe emulsion is acidified after emulsification to reactivate thecatalytic properties of the anionic surfactant.
 17. A process accordingto claim 12, characterised in that the polysiloxane fluid also comprisesan organosiloxane material that reacts with the polysiloxane by a chainextension reaction, and in that a catalyst for the chain extensionreaction is contacted with the polysiloxane either before or after thehigh shear mixer.
 18. A process for making a silicone in water emulsioncomprising mixing a polysiloxane fluid having reactive groups capable oftaking part in a chain extension reaction, a catalyst for said chainextension reaction, at least one surfactant and water and optionally anorganosiloxane material that reacts with said polysiloxane by a chainextension reaction to form a mixture and emulsifying the mixture,characterized in that the polysiloxane fluid, at least one surfactantand water are continuously fed to a high shear mixer in such proportionsas to form a viscous oil in water emulsion which is continuouslywithdrawn from the mixer, the catalyst and the organosiloxane material(if used) each being added either before or after the mixture is fed tothe high shear mixer.
 19. A process according to claim 18, characterisedin that the chain extension reaction is a hydrosilylation reactionbetween the polysiloxane fluid and the said organosiloxane material andthe catalyst is a metal containing catalyst.
 20. A process according toclaim 18 or claim 19, characterised in that the catalyst is added to theemulsion after that emulsion has been formed in the high shear mixer.21. A process according to claim 20, characterised in that the emulsionis diluted with water or aqueous surfactant and the catalyst isincorporated in the water or aqueous surfactant which dilutes theemulsion.
 22. A process according to claim 18 or claim 19, characterisedin that the catalyst is incorporated in the surfactant and/or waterwhich is mixed with the organopolysiloxane before the high shear mixer.23. A process according to claim 18, characterised in that thepolysiloxane fluid is a silanol-functional polydiorganosiloxane and ananionic surfactant having catalytic activity for polymerisation of thesilanol-functional polydiorganosiloxane acts as both surfactant andcatalyst.
 24. A process according to claim 23, characterised in that anamine neutralising agent is contacted with the polysiloxane fluid andanionic surfactant before formation of the emulsion in the high shearmixer and the emulsion is acidified after emulsification to reactivatethe catalytic properties of the anionic surfactant.